Preheat the oven to 400 degrees F (205 C) and place the rice on a baking sheet. Roast the rice for 12-15 minutes, or until the rice is golden brown and smells like popcorn.
Let the rice cool a bit while you prepare the other ingredients, then grind it into a coarse powder (should be like large grains of sand) using a spice grinder, blender, or mortar and pestle.
For the dressing, combine the lime juice, fish sauce, chili flakes and sugar in a small bowl and stir to dissolve the sugar.
Prepare all the vegetables for the salad. For the lettuce you may want to soak the leaves in cold water to crisp them, but be sure to dry them thoroughly before serving. You can put the shallots, scallions, lemongrass, culantro and mint in the same bowl, as they will be going into the pork together.
Add the galangal along with ¼ cup of water to a pan and bring to a boil.
Add the pork and cook, breaking up the meat with a spatula. When the pork is cooked through turn off the heat and dump the pork into a strainer to remove the excess water Pick out the galangal and return the pork to the pan.
Add the dressing, shallots, scallions, lemongrass, culantro and mint and give it a few tosses to evenly distribute. Do not cook the Larb any more.
Plate the Larb Mu and top with some of the toasted rice powder. Serve with the lettuce, additional herbs and wedges of lime.